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BDM-610000050 Rev A Chapter 4: Using the cpuModule 63
Real Time Clock Control
The cpuModule is equipped with a real time clock (RTC) which provides system date and time functions, and
also provides 128 nonvolatile memory locations. The contents of these memory locations are retained whenever
an external backup battery is connected, whether or not system power is connected.
You may access the RTC date, time, and memory using an index and data register at I/O addresses 70h and 71h.
Address 70h is the Index register. It must be written with the number of the register to read or write. Refer to the
map below for valid choices for the index. Data is then written to or read from the selected register by writing or
reading (respectively) the data register at address 71h.
Registers of the RTC are shown below.
.
WARNING
Do NOT change values stored in the RTC registers listed as RESERVED in the table below.
Doing so will interfere with proper cpuModule operation.
Table 47 Real Time Clock Registers
Registers
(hex)
Registers
(decimal)
Number of
Bytes
Function
00h 0 1 BCD Seconds
02h 2 1 BCD Minutes
04h 4 1 BCD Hours
06h 6 1 Day of Week
07h 7 1 Day of Month
08h 8 1 Month
09h 9 1 Year
0A–0Dh 10–13 4 RTC Control Registers
0E–31h 14–49 36 RESERVED—Do not modify!
32h 50 1 BCD Century
33–3Fh 51–63 13 RESERVED—Do not modify!
40–7Fh 64–127 64 User RAM